1. Field of the Invention
The present invention relates to a thermal transfer printer, specifically to a thermal transfer printer that acquires an appropriate contact pressure of the thermal head in correspondence with a printing mode, and produces a good printed image without making printing displacement when printing on a printed medium in different printing modes.
2. Description of the Prior Art
Generally, the thermal transfer printer, pressing a thermal head onto a platen through an ink ribbon and a printed medium such as a printed paper and moving a carriage along the platen, drives a heating element of the thermal head selectively on the basis of printing data, and transfers ink of the ink ribbon onto the printed medium, thus performing printing of a desired image. And, such a thermal transfer printer has been widely employed as an output device for computers or word processors because of its high quality of printed images, low noise, low cost, easiness of maintenance, etc.
FIG. 3 and FIG. 4 illustrate major parts of a thermal transfer printer in general. FIG. 3 is a perspective view of a carriage, and FIG. 4 is a plan view of the drive system of the carriage in FIG. 3.
In FIG. 3 and FIG. 4, on a carriage 5 capable of freely reciprocating along a platen 2 is disposed a motor 14 that drives a mechanism for contacting and detaching a thermal head 6 with a plurality of thermal elements arrayed (not illustrated) to and from the platen 2 and a mechanism for taking up an ink ribbon. A pinion 15 on the output of the motor 14 is engaged with a transfer gear 16. The transfer gear 16 is engaged with a gear 18 formed on the circumference of a cam 17. On the upper side of the cam 17 is formed a cam groove 19 for contacting and detaching the head, and on the lower side thereof is formed a cam groove 20 for taking up the ribbon.
And, a vertical support shaft 21 is installed on the carriage 5 near the platen 2. A substantially T-letter shaped head lever 22 constituting the mechanism for contacting and detaching the head is attached to the support shaft 21 so as to freely swing, serving the support shaft 21 as the fulcrum. A head mount 23 facing to the platen 2 is fastened on a part of the head lever 22 near the platen 2. The thermal head 6 is mounted on a plane of the head mount 23 facing to the platen 2, and a stopper 24 is projected on the head mount 23 with a specific distance from the rear side of the head mount 23.
Further, a head pressing lever 25 of substantially L-letter shape is attached to the support shaft 21 so as to freely rock, serving the support shaft 21 as the fulcrum. On one end of the head pressing lever 25, a pin 26 is projected which is engaged in the cam groove 19 of the cam 17 for contacting and detaching the head. The other end of the head pressing lever 25 is located between the rear side of the head mount 23 on the head lever 22 and the stopper 24, and a spring holding part 27 is formed upright on the other end of the head pressing lever 25. Further, a high contact pressure spring 28 is intervened between the spring holding part 27 and the head mount 23. The energizing force of this high contact pressure spring 28 maintains a state that the head pressing lever 25 is in contact with the stopper 24 on the head lever 22. In this state, the head pressing lever 25 and the head lever 22 are integrally swung by the rotation of the cam 17.
And, the carriage 5 includes a drive gear 30 that is able to freely rotate with the support shaft 31 as the rotation center, which is engaged with a rack 29 formed on the main body of the printer not illustrated. A low contact pressure spring 32 having a lower spring pressure than the high contact pressure spring 28 is bridged between the support shaft 31 and the head lever 22, so as to constantly give to the head lever 22 an energizing force that presses the thermal head 6 toward the platen 2.
Further, the support shaft 31 has a swing plate 33 attached thereon, which is able to freely swing with the support shaft 31 as the fulcrum. A pin 34 is projected on one end of this swing plate 33, which is engaged in the cam groove 20 for taking up the ribbon formed on the lower side of the cam 17. A support shaft 35 is projected on the other end of the swing plate 33, and a transfer gear 36 engaged with the drive gear 30 is attached to this support shaft 35 to freely rotate.
Furthermore, a take-up bobbin 7 and a supply bobbin 8 for the ink ribbon are provided on the carriage 5. As shown in FIG. 4, a take-up gear 37 engaged with the transfer gear 36 is coaxially attached on the lower side of the take-up bobbin 7 through a friction mechanism not illustrate d. And, a second take-up bobbin 38 and a second supply bobbin 39 are provided on the carriage 5. A second take-up gear 41 is coaxially attached on the lower side of the second take-up bobbin 38 through a friction mechanism not illustrated, which is engaged through a transfer gear 40 with the take-up gear 37 on the take-up bobbin 7. The take-up bobbin 7 and the second take-up bobbin 38 are each driven to rotate by the engagement of the transfer gear 36 with the take-up gear 37, which is effected by the swing of the swing plate 33. And, the second supply bobbin 39 is installed on the carriage 5 through a friction mechanism not illustrated.
Further, as shown in FIG. 5, a first cam position 19a, a second cam position 19b, a third cam position 19c, and a fourth cam position 19d are formed in the cam groove 19 of the cam 17 for contacting and detaching the head, in such a manner that the radii from the rotation center of these cam positions 19a, 19b, 19c, 19d are each made into different dimensions r1, r2, r3, r4 within specific ranges of rotation angle. The curve of the cam is formed flat and parallel in each range of the cam positions 19a to 19d,as shown in FIG. 6.
And, by controlling the rotation of the motor 14 in correspondence with the printing mode such as the printing using the thermally fused ink ribbon, the printing using the metallic ink ribbon, or the printing using the thermally sublimed ink ribbon, the rotation angle of the cam 17 is controlled, the cam positions of the cam groove 19 for contacting and detaching the head that the pin 26 on the head pressing lever 25 is engaged with are selected, and thereby the thermal head 6 is made to give an appropriate contact pressure to the platen 2.
That is, the fourth cam position 19d in the cam groove 19 for contacting and detaching the head is the head-up position where the thermal head 6 is detached from the platen 2, the third cam position 19c is the low contact pressure position where the printing is made with the lowest contact pressure, the first cam position 19a is the high contact pressure position where the printing is made with the highest contact pressure, and the second cam position 19b is the intermediate contact pressure position where the printing is made with the intermediate contact pressure between the highest and the lowest. And, in the printing mode using the thermally sublimed ink ribbon, the low contact pressure position is selected, where the pin 26 on the head pressing lever 25 is located at the third cam position 19c in the cam groove 19 for contacting and detaching the head; in the printing mode using the metallic ink ribbon, the intermediate contact pressure position is selected, where the pin 26 on the head pressing lever 25 is located at the second cam position 19b in the cam groove 19; and in the printing mode using the thermally fused ink ribbon, the high contact pressure position is selected, where the pin 26 on the head pressing lever 25 is located at the first cam position 19a in the cam groove 19, where the thermal head 6 is given the highest contact pressure.
Furthermore, a ribbon cassette 44 is mounted on the upper side of the carriage 5, which houses a long ink ribbon 43 and guides the intermediate part of the ink ribbon 43 toward the thermal head 6. This ribbon cassette 44 has a take-up reel and a supply reel not illustrated rotatably installed therein, which are engaged with the take-up bobbin 7 and the supply bobbin 8, respectively, when the ribbon cassette 44 is mounted on the carriage 5. And, the ribbon cassette 44 has a pair of pinch rollers not illustrated installed therein, which are engaged with the second take-up bobbin 38 and the second supply bobbin 39, respectively. Further, the ribbon cassette 44 has a recess 45 formed near the platen 2 on the center thereof, in which the thermal head 6 is inserted; and it has substantially U-letter shaped cutout parts 46, 46 formed on both sides of this recess 45.
As the ink ribbon contained in the ribbon cassette 44, the following types are available: the thermally fused ink ribbon having colored ink layers of the thermally fused yellow, cyan, magenta, and black; the metallic ink ribbon having metallic luster; the thermally sublimed ink ribbon with the thermally sublimed colored ink layers applied thereon; and the ink ribbon having the thermally fused transparent ink layers that are used for undercoat printing or overcoat printing. The type of the ink ribbon 43 is designed to be detected by a selection switch (not illustrated) on the carriage 5 detecting a detection hole formed on the ribbon cassette 44.
Further, as shown in FIG. 7, control means 50 are installed at a specific position on the main body of the printer, which controls the operations of the thermal head 6, head contacting & detaching mechanism, ribbon traveling mechanism, paper feeding mechanism, etc., of this thermal transfer printer 1. The control unit 50 includes a CPU 51, a memory 52 configured with a ROM 52a and a RAM 52b having appropriate capacities, etc., and a controller 53 that controls to drive the foregoing mechanisms of the thermal transfer printer.
The memory 52 stores at least the printing information as the printing data and outputs the printing data to the controller 53, and this controller 53 selectively drives the heating elements of the thermal head 6 in accordance with the printing data.
Further, the memory 52 stores a program that controls the following operations: the current carrying control to the heating elements of the thermal head 6 at least during printing on the basis of the printing data; the contacting and detaching operation of the thermal head 6 to the platen 2; the drive control of the carriage 5; and the carrying operation of a printed paper by the paper feeding mechanism, etc.
The thermal transfer printer thus constructed, receiving printing information from an external device such as a computer not illustrated, performs printing on the basis of printing information.
Further, as mentioned above, if printing is executed using the normal thermally fused ink ribbon, the thermal head will be pressed to the platen with the highest contact pressure. If executed using the thermally sublimed ink ribbon, the thermal head will be pressed with the lowest contact pressure. And, if executed using the metallic ink ribbon, the printing will be executed with the intermediate contact pressure between the former two. Further, the contact pressures of the thermal head to the platen are selected by controlling the rotational positions of the cam 17.
And, there is a case that requires printing with different contact pressures of the thermal head to the platen on a piece of printed paper, for example, printing with the thermally fused ink ribbon and the metallic ink ribbon, printing with the thermally sublimed ink ribbon and the metallic ink ribbon, or the like.
However, when printing is conducted with different contact pressures on a piece of printed paper, that is, when after printing is conducted with a high contact pressure, printing with a low contact pressure is overlapped at the same printing position, or when after printing with a low contact pressure, printing with a high contact pressure is overlapped at the same printing position, the printing position is displaced in the paper feeding direction, because the printing position during the head pressed down is dislocated downward in printing with a low contract pressure in comparison to printing with a high contact pressure, or the printing position during the head pressed down is dislocated upward in printing with a high contract pressure in comparison to printing with a low contact pressure. The printed results in these two cases become inadequate in quality, as shown in FIG. 8A and FIG. 8B.
FIG. 8A illustrates printing with the intermediate contact pressure after printing with the high contact pressure, in which the subsequent printing with the intermediate contact pressure is dislocated in the feeding direction of printed paper, namely, in the printing direction, against the preceding printing with the high contact pressure. On the other hand, FIG. 8B illustrates printing with the high contact pressure after printing with the intermediate contact pressure, in which the subsequent printing with the high contact pressure is dislocated in the opposite direction to the feeding direction of printed paper, against the preceding printing with the intermediate contact pressure.
Furthermore, when printing with a low contact pressure is overlapped at the same printing position after printing with a high contact pressure, or when printing with a high contact pressure is overlapped at the same printing position after printing with a low contact pressure, the printing position is displaced in the lateral direction, namely, in the moving direction of the thermal head, because the transfer position of the ink ribbon during the head pressed down is displaced more significantly in the direction of shifting in printing with a high contract pressure than in printing with a low contact pressure, on the other hand, the transfer position of the ink ribbon during the head pressed down is displaced less significantly in the direction of column in printing with a low contract pressure than in printing with a high contact pressure. The printed result becomes inadequate in quality, as shown in FIG. 9, which is a problem to be resolved.